2027 ICD-10-CM Diagnosis Code M86.661Other chronic osteomyelitis, right tibia and fibula
ICD-10-CM Codes›M00–M99›M86-M90›M86
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 92
- Not Chronic
M86.661 is a billable ICD-10-CM diagnosis code for other chronic osteomyelitis, right tibia and fibula. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 400, 539 through 541. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 221 closely related codes. Coders also document this condition as chronic osteomyelitis of lower leg. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Osteomyelitis.
For Medicare Advantage risk adjustment, M86.661 maps to CMS-HCC Category 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis) under the V28 model, adding a risk factor of about 0.479 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
M86.661 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.
Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Chronic osteomyelitis of lower leg
- Chronic osteomyelitis of right lower leg
- Chronic osteomyelitis of right tibia
- Chronic osteomyelitis of tibia
- Osteomyelitis of right tibia
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to M86.661: its own notes plus those printed at M86, block M86-M90, and Chapter 13. A note printed at a category, block or chapter applies to every code under it.
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
- postprocedural osteopathies (M96.-)
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
- arthropathic psoriasis (L40.5-)
- certain conditions originating in the perinatal period (P04-P96)
- certain infectious and parasitic diseases (A00-B99)
- compartment syndrome (traumatic) (T79.A-)
- complications of pregnancy, childbirth and the puerperium (O00-O9A)
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
- endocrine, nutritional and metabolic diseases (E00-E88)
- injury, poisoning and certain other consequences of external causes (S00-T88)
- neoplasms (C00-D49)
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
Use Additional Code
Add a second code, after this one, to fully describe the condition.
Notes
General instructions on how these codes are used.
- Use an external cause code following the code for the musculoskeletal condition, if applicable, to identify the cause of the musculoskeletal condition
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name M86.661, its category, or a range that includes it.
Code First 1
These codes say to code first a condition named in the note, and M86.661 is one of the conditions named.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Osteomyelitis
inflammation of the bone as a result of infection. it may be caused by a variety of infectious agents, especially pyogenic (pus - producing) bacteria.
Patient EducationClinical
Bone Infections
Like other parts of the body, bones can get infected. The infections are usually bacterial, but can also be fungal. They may spread to the bone from nearby skin or muscles, or from another part of the body through the bloodstream.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert M86.661 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About M86.661Overview
What is the ICD-10 code for other chronic osteomyelitis, right tibia and fibula?
The ICD-10-CM code for other chronic osteomyelitis, right tibia and fibula is M86.661 (sometimes written as M86661). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is M86.661 (Other chronic osteomyelitis, tibia and fibula) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report other chronic osteomyelitis, right tibia and fibula on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does M86.661 group to?
When other chronic osteomyelitis, right tibia and fibula is the principal diagnosis on an inpatient stay, it groups to MS-DRG 541, 400, 539, 540, with relative weights from 0.8293 to 2.0249 depending on complications. Higher weights mean higher Medicare reimbursement.
Is M86.661 a CC or MCC?
CMS lists M86.661 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 221 closely related codes in its exclusion list.
Can M86.661 be reported with B67.2?
Not as a rule. The Excludes1 note at M86, which applies to M86.661, lists "echinococcus (B67.2)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
What HCC is M86.661?
M86.661 (other chronic osteomyelitis, right tibia and fibula) maps to CMS-HCC Category 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis), commonly written as HCC 92, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 39 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. It does not map to any RxHCC in the Part D prescription drug model.
Does M86.661 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, M86.661 adds a risk adjustment factor of about 0.479 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.471 to 0.632 depending on the payment segment). HCC 92 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 92 category page.
